Holography has been used widely in a variety of applications to reproduce three-dimensional images. U.S. Pat. No. 4,589,686 describes usage for anti-counterfeiting purposes such as on credit cards, probably the most widely recognized use at the present time. The same patent also discloses many other patents relating to diffraction grating patterns and three-dimensional images of objects and scenes. The cover of the National Geographic issue of March, 1984, is another example of use to increase the attractiveness of the magazine to the observer. The same issue of the National Geographic contains a good description of holography.
The first successful use of holographic materials on fabrics was originally disclosed in my U.S. Patent No. 4,838,965. Since that time two other U.S. Pat. Nos. 4,956,040 and 5,073,222 have issued to another inventor. The methods of these two more recent patents achieve resistance to repeated washing by enveloping a precut hologram between a clear polyester coating and an adhesive scrim backing and then adhering the resulting laminate to wearing apparel with the adhesive in the scrim. The addition of a separate polyester layer on top of the hologram and scrim underneath adds two layers which reduce flexibility and increase stiffness in a product where a "soft hand" is highly preferable. In addition the separate polyester layer of this pouch or envelope that is not embossed interferes with the clarity of the holographic image.
Still another example of the use of sealing holographic products at the perimeter to prevent the hologram from being attacked by water can be found in U.S. Pat. No. 5,095,375. This patent utilizes a polymer or metal film bound by an adhesive to the perimeter of two substrates (for example, glass substrates) that thereby fully enclose or encapsulate a water sensitive hologram. The product of the present invention can be affixed to a single glass substrate and accomplish substantially the same result.
The holograms and diffraction gratings disclosed in my U.S. Pat. No. 4,838,965 as well as many of those manufactured and sold today for application to various substrates are multi-layered products. Although other layers may be present depending on the manufacturer, most of these products contain a plastic carrier, a reflective intermediate surface or layer, and an adhesive backing. The adhesive material is often activated by heat and pressure to attach the holographic materials to appropriate substrates and is generally referred to as an iron-on adhesive. Pressure sensitive and contact adhesives are also used especially where the holographic materials are intended for attachment to paper substrates for labeling or advertising purposes. The embossed surface of the metallized plastic carrier disclosed in U.S. Pat. No. 4,838,965 actually reproduces the three-dimensional image or pattern when light is reflected through the transparent plastic by the metallic layer. This means of reproduction is most commonly referred to as embossed holography. A more complete description can be found in Chapter 9 of Holography Marketplace, Ross Books, March, 1991. These holograms and diffraction gratings are generally available in sheets of film or foil bearing images or patterns on a repetitive or continuous basis throughout their length and breadth. The sheets are at least six inches wide and are usually sold in rolls up to two hundred feet long. The purchaser can cut the images or patterns out of the sheets to suit his needs. For example, the hologram of the Golden Gate bridge depicted in my U.S. Pat. No. 4,838,965 would be repeated throughout a commercially available sheet bearing many reproductions of that holographic image. The purchaser can cut each image of the bridge out of the sheet and attach it to whatever substrate he deems appropriate for his purposes. For example, such holograms can be affixed by the mechanized hot stamping process to the paper cover of a magazine such as the above National Geographic issue while the manual pressure sensitive process would be suitable for small quantities.
Strictly speaking, a diffraction grating or the related micro-etching or color explosion are not holograms but the commercially available versions employ the same multi-layered structure as an embossed hologram. The purpose of such products is to create the illusion of depth and motion as light is diffracted from the surface of the material without the prohibitive expense of originating holographic master plates. Diffraction grating requires a master grating to make a die which produces a replica of the grating in the metallized film. Micro-etching transfers line art or a continuous tone photograph to a master die for creating an image by using graphic screens. The color explosion employs what is known in the graphic arts industry as stepping to include drop down, side step, dimensional side step, rotation in varying degrees and back up. These techniques enable the customer to choose from a wide variety of options to achieve different visual effects. The multi-layered structure in all products requires a layer of adhesive on the back for protecting the reflective layer as well as the adhesion characteristic necessary for bonding to various substrates with heat and pressure. Since the problems associated with the structure of all these holographic materials are essentially the same with or without attachment to a substrate, they are considered to be equivalents of the hologram for purposes of the present invention. The word "holographic" when used in this specification in combination with words such as "products", "materials" or "films" can be taken to include holograms, diffraction gratings, micro-etchings, color explosions or any other light reflecting product having the same multi-layered structure.
Another more recent development in the holography industry involves a demetallized holographic foil suitable for application to various substrates requiring limited laundry or dry cleaning. This structure eliminates approximately 78 to 80% of the reflective metal layer. The resulting product reflects subtle pastels creating a fashionable yet less metallic look with a glamorous appearance. When paired with a appropriate double-sided adhesive coated heat sealable film, it becomes a heat transfer foil. Presently Sealtran Corporation, Chicago, Ill., 60614 manufactures this double-sided adhesive coated film known as AD as an attractive laminated pouch for drivers licenses, bus passes and other letter size envelopes or pouches. For the purpose of this invention this same material can add a decorative accent to textiles and other substrates by using it as a cold peel heat transfer foil or integrating it into a heat transfer design. The concept of transfers is not new but using demetallized or other holographic materials with sealed edges alone or as a component of a larger design is new. This material can be used as the sole decoration on fabric by placing the desired shape of the demetalized holographic material in registration with the same shape of the double-sided adhesive coated film on the fabric with the textile adhesive side in contact with the fabric and the AD adhesive side in contact with the holographic material. This completed assembly is covered with silicone paper and sealed in place by a heat press with medium pressure and a temperature of about 300 degrees Fahrenheit for about 8 seconds. After cooling the paper is peeled away exposing the metallized holographic imagery. Although fragile to various environmental conditions, it can withstand limited washing if hung to air dry. The finished product offers the customer an enhanced focal point with drawing power.
Security devices such as the Visa and Mastercard credit cards displaying reflective holograms have been used for approximately nine years and although they still have security value provided by the integrated hologram, the current trend is toward the use of clear holography on credit cards offering transparency with greater reflectivity. These holograms are comprised of a multi-layered material to include a synthetic carrier, a sandwiched reflective layer and an adhesive back. However the interposed reflective material is not metallized but a complex, silicone-based chemical compound which provides an optical coating. Although presently expensive as a security measure, a clear hologram permits the viewer to see imagery, numbers, letters or symbols on the substrate to which it is attached thereby providing another security capability for the security industry. The reflective sandwiched layer, regardless of its composition, requires protection from damaging environmental forces. This can be accomplished by sealing the edges. The equipment making clear holography possible is manufactured by Datacard in Havant, UK and Holland and marketed as recently as October, 1992.
While the prior art provides holographic materials for attachment to substrates, it does not provide such materials that can be readily and inexpensively attached to substrates that will be exposed to the strenuous conditions of ordinary use. Even ordinary environmental insults such as rain, humidity, heat, cold, and wind will affect the quality of the embossed surface after a period of time if not protected by sealing the edges. Holographic products are especially unsatisfactory for attachment to clothing which will be repeatedly subjected to washing, drying and even dry cleaning. Even my earliest processes for dealing with this problem, although advancements over the prior art of their day, were more cumbersome and expensive and the edges of the resulting products were not sealed as consistently as would be desirable.
The present invention differs from my previous inventions in the use of a broader class of adhesives including contact and pressure sensitive adhesives and even adhesives that are not completely impervious to moisture. I have discovered that sealing the edge of holographic materials that will eventually be attached to either moisture permeable or moisture impermeable substrates still results in a product that withstands abrasion better and resists deterioration from exposure to moisture better than the same holographic materials without a sealed edge.